Baffle to reduce azimuthal etch asymmetry

ABSTRACT

Systems and techniques for improving azimuthal symmetry in an etch process are described. In some implementations, a baffle may be used to modify the flow of gas in an etch process. A baffle may include a baffle wall, which may have at least two regions of equal radial extent. A first region may have a first open area percentage, while a fourth region may have a fourth open area percentage. The first open area percentage is smaller than the fourth open area percentage. The baffle may be positioned so that the first region is toward a vacuum inlet.

BACKGROUND

Semiconductor devices are generally fabricated using a sequence of processes to form successive device layers on a substrate such as a silicon wafer.

An etch process is commonly used. In an etch process, material is removed from one or more regions of the substrate in order to fabricate a device with a desired configuration.

Process uniformity and reproducibility are important, so that device characteristics are uniform for devices fabricated on different wafers and on different regions of the same wafer. If, for example, an etch process is non-uniform across a wafer, some regions will be etched either more or less than desired. The resulting devices may thus function differently than identically designed devices on the same wafer.

DESCRIPTION OF DRAWINGS

FIG. 1 is a side view of an etch system according to the prior art.

FIG. 2A is a side view of an etch system, according to an embodiment.

FIG. 2B is a top view of an etch system, according to an embodiment.

FIG. 3A is a top view of a baffle, according to an embodiment.

FIG. 3B is a two-dimensional side view of a baffle, according to an embodiment.

FIG. 3C is a two-dimensional side view of a baffle, according to another embodiment.

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Systems and techniques described herein may be used to improve etch rate uniformity. In a dry etch process, material is removed from a substrate by chemical and/or physical interaction between an etchant material and the substrate material.

The etch rate (the amount of material removed from the substrate per unit time) depends on etchant characteristics, such as the etchant temperature, pressure, and distribution.

FIG. 1 shows an etch system 100. System 100 includes a chamber 105 with an interior region 110. The pressure of interior region 110 may be reduced using a vacuum generator such as turbopump 120 via a vacuum inlet 125. System 100 may include a magnet such as an electromagnet 130 including one or more coils 132. The magnet may be used to control the flow of etchant gases from one or more etch gas sources 140 toward a wafer 150 on a wafer support 155.

Characteristics of system 100 may affect the etch process across wafer 150. For example, the current inventors recognized that the relative placement of turbopump 120 may disturb the symmetry of the distribution of etch gas density, speed, temperature, or other etch gas parameters at the surface of wafer 150. Such an asymmetric distribution may lead to an unacceptable level of etch rate asymmetry.

FIG. 2A shows an etch system 200 for improved etch rate symmetry. In system 200, a flow modulator such as a baffle 260 is positioned proximate to wafer 250 on a wafer support 255 to change the flow of gases in chamber 205 to improve the symmetry of the etch process.

Baffle 260 may include positioning features so that baffle 260 may be positioned with respect to a base portion 215 of chamber 205. Particularly, baffle 260 may be positioned in a desired orientation with respect to a vacuum inlet 225. For example, baffle 260 may be affixed to the base portion 215 of chamber 205 via through holes in a base flange 270, may be affixed to a different portion of the system or may be positioned without being fixed.

Baffle 260 may comprise a material that is not substantially degraded by the etch process to be used in chamber 205. For example, baffle 260 may be made of or coated with stainless steel and/or titanium. Other materials may be used as well.

FIG. 2B shows a top view of a portion of system 200, illustrating the relative positions of wafer holder 255, baffle 260, and inlet 225. For illustrative purposes (see below), baffle 260 is said to include four regions of the baffle wall, a first region 271, a second region 272, a third region 273, and a fourth region 274, which may be described by their relationship to a radial axis 275. Each of the four regions is of equal radial extent.

Note that FIG. 2B does not illustrate a bottom flange portion of baffle 260. In such an implementation, other methods of positioning baffle 260 may be used. For example, the shape of baffle 260 may be non-uniform. Baffle 260 may be positioned in system 200 by aligning a feature such as feature 277 with a complementary feature (e.g., a groove) in the base portion 215 of chamber 205. Of course, other implementations are possible.

FIG. 3A shows a top view of baffle 260, and FIG. 3B shows a two dimensional side view of baffle 260. In FIG. 3A, positioning features 265 comprise a number of through holes for mounting screws in a base flange 270 of baffle 260, so that baffle 260 may be secured to base portion 215 of chamber 205. Positioning features 265 include features 265A, 265B, and 265C. Rather than being spaced equidistant from features 265B and 265C, FIG. 3A illustrates an implementation where feature 265A is closer to feature 265B than to 265C. Thus, positioning features 265 enable baffle 260 to be positioned in the correct orientation for a particular etch chamber configuration.

Baffle 260 also includes a baffle wall 280, which may be generally perpendicular to base flange 270 (i.e., generally perpendicular to the plane of the page of FIG. 3A). Baffle wall 280 may be said to include four quadrants, denoted as first region 271, second region 272, third region 273, and fourth region 274. Note that the regions are defined as shown for illustrative purposes only.

In FIG. 3A, radial axis 275 is defined as shown. With respect to radial axis 275, first region 271 extends from −45 degrees to +45 degrees, third region 273 extends from +45 degrees to +135 degrees, fourth region 274 extends from +135 degrees to −135 degrees, and second region 272 extends from −135 degrees to −45 degrees. Each region extends from a bottom edge to a top edge of baffle wall 280. Note that although baffle 260 is shown as generally cylindrical, it can be of any desired shape.

FIG. 3B shows a two dimensional side view of baffle 260. Baffle wall 280 includes at least one opening 282, and may additionally include one or more other openings 283 (e.g., cutouts in baffle wall 280 for passage of a robot arm to access a wafer). Note that for the case of cutouts, the top edge of baffle wall 280 for determining the area of each region may be considered the extension of the top edge of the baffle on either side of the cutout, as shown by the dashed lines in FIG. 3B.

Openings 282 and 283 are sized and positioned in baffle wall 280 to improve the azimuthal symmetry of an etch process. FIG. 3B illustrates a non-uniform radial distribution of relative open area on baffle wall 280. That is, the percentage of baffle wall that is open (which may be referred to as the region's open area percentage) increases from first region 271 to second region 272 and third region 273, and also from second region 272 and third region 273 to fourth region 274.

Note that the open area percentage may be calculated as follows. Referring to region 272 of FIG. 3B, the total area A_(total) of the region may be defined as the width W multiplied by the height H of the region. The open area A_(open) may be defined as the sum of the open areas A₁, A₂, and A₃. The open area percentage of region 272 is thus the ratio A_(open)/A_(total).

Note also that although the openings 282 in second region 272 and third region 273 are shown as being the same, in some implementations the relative open area and/or the shape or distribution of openings 282 may be different in second region 272 than in the third region 273. For example, FIG. 3C shows a second region 272 having a different open area percentage than a third region 273.

Referring again to FIG. 2B, baffle 260 is positioned so that the first region 271 is oriented toward inlet 225. That is, the region with the smallest relative open area is oriented toward inlet 225, while regions of greater relative open area are oriented further from inlet 225, and the region of the greatest relative open area is oriented away from inlet 225.

Note that the definition of the regions may be different than that shown. Referring again to FIG. 3C, the boundaries of the regions may be shifted by an amount Δ, so that the open area percentage of first region 271 is still smaller than the open area percentages of regions 272, 273, and 274, but the smallest possible quadrant need not be positioned exactly toward inlet 225.

Many possible implementations of baffle 260 may be used. In FIG. 3B, a small number of openings 282, each having a fairly large opening size, are shown. In other implementations, more openings may be used, and at least some of them may be relatively smaller. In some implementations, a single opening that increases in size as the radial distance from inlet 225 increases may be used.

As noted above, the first through fourth regions are defined for illustrative purposes. Baffle 260 may be divided differently; for example, into six regions, seven regions, twelve regions, and so forth. In general, the relative open area is smallest in the one or more regions closest to inlet 225 and increases as the radial distance from inlet 225 increases. Note also that if more regions are defined (or radially smaller regions), the relative open area may fluctuate due to the coarseness of the openings, and the relative open area should be determined taking the coarseness of the openings into account.

The current inventors recognized that an additional benefit may be obtained by providing a keying feature for baffle 260. Etch rate asymmetries may be highly dependent on the configuration of the chamber being used, so one or more keying features may be provided to position baffle 260 in the system.

For example, positioning features 265 of FIG. 3A may be different for baffles to be mounted in different etch chamber configurations. Similarly, feature 277 of FIG. 2B may be shaped or positioned differently for different etch chamber configurations.

A number of implementations have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. For example, the baffle may not be continuous. That is, a region such as the fourth region (furthest from the inlet) may be entirely open, so an interior region “surrounded” by the baffle is not surrounded by material on all sides. The portion of the baffle wall that is open thus corresponds to a relative open area of 100%. Note also that the regions referred to above are defined as substantially equal in radial extent so that the open areas among different regions may be compared. Accordingly, other implementations are within the scope of the following claims. 

1. A baffle comprising: a baffle wall having at least some open area, the baffle wall comprising a plurality of regions each having an associated radial extent and an associated open area percentage equal to the percentage of the area of the region that is open area, the plurality of regions including a first region having a first open area percentage and a fourth region having a fourth open area percentage greater than the first open area percentage, the fourth region having an associated radial extent substantially equal to the associated radial extent of the first region; and positioning features configured to position the baffle in an etch chamber including a vacuum inlet, the positioning features to position the first region of the baffle wall toward the vacuum inlet.
 2. The baffle of claim 1, further comprising a base flange portion.
 3. The baffle of claim 2, wherein the positioning features are included in the base flange portion.
 4. The baffle of claim 1, wherein the associated radial extent of the first region is 90 degrees.
 5. The baffle of claim 1, wherein the associated radial extent of the first region is less than 90 degrees.
 6. The baffle of claim 5, wherein the associated radial extent of the first region is equal to or greater than 30 degrees.
 7. The baffle of claim 1, wherein the plurality of regions includes a second region, the associated radial extent of the second region substantially equal to the associated radial extent of the first region and the fourth region, the second region between the first region and the second region, the second region having a second open area percentage greater than the first open area percentage.
 8. The baffle of claim 7, wherein the second open area percentage is less than the fourth open area percentage.
 9. A system, comprising: an etch chamber; a wafer holder positioned in the etch chamber; a vacuum inlet in communication with the wafer holder to enable removal of gas from the etch chamber; and a baffle including a baffle wall surrounding the wafer holder, a portion of the baffle wall positioned between the wafer holder and the vacuum inlet; wherein the baffle wall comprises a plurality of regions, each having an associated radial extent and an associated open area percentage equal to the percentage of the area of the region that is open area, the plurality of regions including a first region having a first open area percentage and a fourth region having a fourth open area percentage greater than the first open area percentage, the fourth region having an associated radial extent substantially equal to the associated radial extent of the first region, and wherein the baffle is positioned so that the first region is positioned toward the vacuum inlet and the fourth region is positioned away from the vacuum inlet.
 10. The system of claim 9, wherein the baffle further comprises positioning features configured to position the baffle in the etch chamber, the positioning features to position the first region of the baffle wall toward the vacuum inlet.
 11. The system of claim 9, further comprising a vacuum generator in communication with the vacuum inlet.
 12. The system of claim 11, wherein the vacuum generator is a turbopump.
 13. The system of claim 9, wherein the baffle comprises a material that is not substantially degraded by an etch process associated with the etch chamber.
 14. The system of claim 13, wherein the material includes at least one of stainless steel and titanium.
 15. A baffle, comprising: a baffle wall, the baffle wall having a top edge and a bottom edge, the baffle further having at least two regions of substantially equal radial extent, the at least two regions further extending from the top edge of the baffle to the bottom edge of the baffle, wherein the at least two regions each have an associated open area; positioning features configured to position the baffle in an etch chamber including a vacuum inlet, the positioning features to position a first region of the at least two regions toward the vacuum inlet, wherein the first region has a minimum associated open area of the at least two regions.
 16. The baffle of claim 15, wherein the at least two regions further includes a fourth region opposite the first region, the fourth region having a maximum associated open area of the two or more regions.
 17. The baffle of claim 15, further including a second region positioned between the first region and the fourth region and having an associated open area greater than the minimum associated area and less than the maximum associated area.
 18. The baffle of claim 17, further including a third region positioned between the first region and the fourth region and having an associated open area greater than the minimum associated area and less than the maximum associated area.
 19. The baffle of claim 18, wherein the associated open area of the second region is equal to the associated open area of the third region.
 20. The baffle of claim 18, wherein the associated open area of the second region is the same as the associated open area of the third region.
 21. The baffle of claim 18, wherein the radial extent is 90 degrees. 